ASoC: SOF: IPC4: Introduce message handling functionality

ASoC: SOF: IPC4: Introduce message handling functionality

Merge series from Peter Ujfalusi <peter.ujfalusi@linux.intel.com>:

The series adds the basic IPC4 message handling code, implementing the ipc
callbacks.
Due to the difference between IPC3 and IPC4 messaging we need to introduce new
message container for IPC4, but the SOF internal callbacks and structures can be
kept as they were and leaving it for the IPC specific code to handle the
differences.

The series provides the foundation for both lowe level (sound/soc/sof/intel) and
high level IPC4 implementation (topologies, firmware loading, control handling,
etc).